Most infections by viruses and other intracellular pathogens are countered in the human host by a combination of humoral (antibody) and cellular (lymphocyte and phagocyte) immune effectors. Although the precise identity of immune effectors capable of protecting the host against some chronic intracellular pathogens (e.g. HIV-1) remains unknown, attempts to develop preventive and therapeutic vaccines still focus on the induction of appropriate humoral and cellular immune responses. Furthermore, since most human viral pathogens (including HIV-1) are transmitted across mucosal surfaces, it is important that vaccines induce such responses locally (at the mucosal surface) as well as systemically and that they are durable for long-term protection.
The issues of durability and mucosal immunogenicity have been previously addressed by encapsulating vaccine antigens in appropriately-sized biodegradable, biocompatible microspheres made of lactide/glycolide copolymer (the same materials used in resorbable sutures). It has been shown that such microspheres can be made to release their load in a controlled manner over a prolonged period of time and can facilitate the interaction of their contents with the local immune system when administrated mucosally.
In the case of HIV-1 infection, there is insufficient information at this time regrading the virus and its interactions with the human immune system to permit the rational design of a preventive vaccine. However, it has been noted that many candidate HIV vaccines tested to date fail to elicit antibodies capable of neutralizing wild-type HIV-1 or binding to native HIV-1 proteins, fail to induce a substantial population of effector cells capable of destroying HIV-1-infected cells, and fail to induce significant responses at mucosal surfaces. A possible approach to overcoming these problems (applicable to both HIV-1 and other chronic intracellular pathogens) is to identify a native protein, accessible to the immune system on the surface of both free virus and infected cells, and present it to the immune system (systemic and mucosal) encapsulated in microspheres to protect and augment its immunogenicity.